Thanks everyone for your contributions.
Is it possible that if the hum originates in the power supply section that it would only (or more accurately, mostly) be heard through the left speaker? This is asked in a spirit of enquiry 🙂
As mentioned earlier, when a source is played through Aux or Tuner it sounds very good and balanced through both channels.
Is it possible that if the hum originates in the power supply section that it would only (or more accurately, mostly) be heard through the left speaker? This is asked in a spirit of enquiry 🙂
As mentioned earlier, when a source is played through Aux or Tuner it sounds very good and balanced through both channels.
If... the hum is caused by a faulty cap, am I right in thinking that the only way to determine this is to replace each cap and see if at some point I replace the bad one and the hum ceases? A recap of a whole section might be quicker? Please could you let me know the most efficient way of detecting and fixing a faulty cap situation.
Cleaning the contacts and resolders can only remedy a defect when the signal is missing. Electrolytic capacitors cause brum, hum, low frequency oscillations. Depending on the sensitivity the hum will be visible on the oscilloscope. I restored a lot of C-4, C-2, C-2a, and at all I changed absolutely all electrolytic capacitors and the performances were measured exactly according to the service manual.
How old is it? Sure it is not just the PS caps? Did it start all at once , or build up over time?
Thanks guys. I only have a DMM and a cheap transistor tester, but no oscilloscope.
This unit was recently purchased secondhand and the hum was present.
The hum’s quality has changed slightly following servicing of the wafer switches and reflowing of solder wherever it visually looked necessary.
So it’s still present and the most likely candidate now is a, or some, faulty caps.
As mentioned, it sounds very good, so if I could detect and replace the faulty cap(s) I would, and just enjoy it’s sound for a while. I’d prefer to do the full recap a bit further down the road. Having fully recapped a P2200 and a CR1020 I appreciate how fantastic a unit can sound afterwards.
Am I right in thinking that there isn’t a method or to detect which cap is faulty? Freeze spray? Tapping each one and hoping the bad one might cause the hum to change it’s sound? Or any other techniques?
This unit was recently purchased secondhand and the hum was present.
The hum’s quality has changed slightly following servicing of the wafer switches and reflowing of solder wherever it visually looked necessary.
So it’s still present and the most likely candidate now is a, or some, faulty caps.
As mentioned, it sounds very good, so if I could detect and replace the faulty cap(s) I would, and just enjoy it’s sound for a while. I’d prefer to do the full recap a bit further down the road. Having fully recapped a P2200 and a CR1020 I appreciate how fantastic a unit can sound afterwards.
Am I right in thinking that there isn’t a method or to detect which cap is faulty? Freeze spray? Tapping each one and hoping the bad one might cause the hum to change it’s sound? Or any other techniques?
Power supply cap issues often cause problems and a recap there is excellent advice but in my case does the loudness of the hum through the left channel suggest that the faulty cap is more likely in one channel on another function board?
Maybe. Most amps are not wired identically and the ground paths may differ making one channel more sensitive.
Does that unit use wire wrap terminals or any internal push on connectors? One could be corroded. I guess the on-board bypass cap for one channel could be to blame, though I rather think it is still a bad ground. De-Oxit all the connectors and switches? Wiggling and tapping is always good. I doubt freeze spray will find anything unless it changes from the second you turn it on and the hum builds. How did they do the central DCC to chassis ground? A screw on one of the board posts?
Guess you know why it was for sale. I have had good luck with hi-fi used, but every single piece of semi-pro sound equipment I ever bought was faulty, and it was clear the seller knew it. Fortunately, I fixed all of it.
Does that unit use wire wrap terminals or any internal push on connectors? One could be corroded. I guess the on-board bypass cap for one channel could be to blame, though I rather think it is still a bad ground. De-Oxit all the connectors and switches? Wiggling and tapping is always good. I doubt freeze spray will find anything unless it changes from the second you turn it on and the hum builds. How did they do the central DCC to chassis ground? A screw on one of the board posts?
Guess you know why it was for sale. I have had good luck with hi-fi used, but every single piece of semi-pro sound equipment I ever bought was faulty, and it was clear the seller knew it. Fortunately, I fixed all of it.
Thanks for the extra info and advice.
Gradually checking through the boards.
Could you tell me where (which caps) the following is located “on-board bypass cap for one channel?”
I’ll check this out, “How did they do the central DCC to chassis ground?”
Without seeing it myself, hard to go further. I never knew how I fixed things. Just seem to stumble on to them.
There are those who can design, those who build, and those of us who can fix. I can teach how to design, show how to build, but never was able to train a tech that innate ability to fix. When I interviewed kids out of tech school, my trick question was " What do you do if your washer breaks" Almost uniformly, the 4.0 average students say "Call Sears" and the rest look at me stupid and say "I fix it" . I hired them. The first ones I could teach the machine, but not how to fix.
There are those who can design, those who build, and those of us who can fix. I can teach how to design, show how to build, but never was able to train a tech that innate ability to fix. When I interviewed kids out of tech school, my trick question was " What do you do if your washer breaks" Almost uniformly, the 4.0 average students say "Call Sears" and the rest look at me stupid and say "I fix it" . I hired them. The first ones I could teach the machine, but not how to fix.
I have worked on a C4 that would intermittently shunt down. After troubleshooting I noticed the regulated power supply (negative side) would current limit and shut down the amplifier. I know this is not your problem but I want to let you know that Yamaha used the problematic VD1212 double diodes throughout the amplifier. There are 10 in total....D127 and D128, D301 and D302, D318, D311, D601 and D602. There are another two located in the phono amp that do not have any silkscreen marking on the board so be careful to note the polarity before removing. I tried to systematically troubleshoot the amp for six months but it was so intermittent I could never find the problem. Finally I replaced all 10 of the VD1212 diodes with two series connected 1N4148 diodes and the amp have worked flawlessly ever since. This may not fix your problem but it is worth a try and is good preventative maintenance.
Regards Bob
Regards Bob
My opinion is that you are wasting your time looking for the cause of the defect, in addition, you don't even have measuring equipment. Change all electrolytic capacitors and resolder all boards.
Thanks everyone. Appreciate the advice from all quarters, I really want to solve this issue. So, I’m going to reflow solder and change the caps in the power supply first. This doesn’t preclude me from doing the same in the other sections in the near future. Just want to hear it as it is without the hum to start with.
Fingers crossed.
Fingers crossed.